Auxiliary handle inventions which provide ergonomic benefit to hand manipulated implements are well known. However, most have one or more drawbacks which limit their usefulness and ability to accomplish the objectives for which they were conceived. Some auxiliary handles are pivotally mounted and some are mounted using free moving rings or ropes or wires, and some use omnidirectional-motion-enabling springs and like elements to accomplish connection and useful purpose.
Most auxiliary handles for implements are difficult for manufacturers to build and install, or for users to install without making modifications to the implement or without the need for tools. The handles often are typically awkward to use, lack suitable adjustment means for differing users or changing task conditions, interfere with the conventional use of the implement, add to the weight of the implement, or suffer from a lack of freedom of desired movement, which then leads to ergonomic strain and fatigue, poor work quality, and productivity loss. The majority of auxiliary handles seem to suffer from some significant shortfall or another. The examples which follow explain some of the advantages and difficulties.
The earliest and most familiar designs that are widely recognized are the pivotally attached auxiliary handles. These are good for obtaining leverage for lifting and lowering implements yet are typically difficult to install without tools, add to the weight of the implement, are costly to manufacture, are susceptible to corrosion, and interfere with storage or transportation. More importantly, however, these designs cause the working head of the implement to change orientation with respect to the ground if the auxiliary hand grip is moved laterally during use. Such occurrence often results in unintentional tool action such as dumping a load when using a shovel or undesirably scalping the ground and producing hazardous flying debris in the case of a vegetation trimmer. As well, such characteristics often require a user to adopt unusual motions or posture to avoid such effects and result in early fatigue and soreness while general work quality and productivity suffers. Such combination of characteristics makes the pivotal design suitable for only a few special tasks and hence is rarely seen in the general marketplace.
To overcome these effects, new handle designs were developed that eliminated the implement's reorientation effect when the auxiliary hand grip was moved laterally. These are comprised mainly of swivellable collars and linkages, swivellable wires, as in Bickley U.S. Pat. No. 2,521,441, swivellable rings, or various innovative combinations of these as in Clark U.S. Pat. No. 6,062,619. Other designs toward such goal include simple ropes, and bungee cord type configurations. These inventions successfully provide a wide range of motion and freedom yet so much so that in practice they are generally unstable. An interesting feature of these designs is that they require a user to continuously balance the implement. Curiously, the balancing force can only arise from the hand which grips the implement itself since the grip-hand holding the auxiliary handle cannot exert any stabilizing force because of its high degree of freedom of motion laterally. This effect also means that any loading of the implement must be balanced by the single hand gripping and operating on the implement itself. Typically the motion control task of this hand involves muscles of the forearm and wrist using a twisting action which reverses frequently according to the implement's dynamic balancing needs, and is accomplished while this hand is gripping in relatively tight fashion so to be ready for response to the highly varying loading conditions. For shoveling, this results in significant ergonomic strain by placing a relatively large and continuous yet rapidly varying load force requirement upon relatively weak muscle groups and systems of the wrist and forearm, and typically with minimal periods for rest, a condition-set which is generally known as an ergonomically undesirable practice. Relief is possible if one switches hands, however such action is inconvenient and awkward and results in productivity loss due to differences in skill when using one hand versus another, in the time and effort taken to make the switch, and in the opportunity available to drop the auxiliary handle during the switch.
Another important and less desirable aspect of these designs is that, due to their omnidirectional nature, the auxiliary grip handle must be continuously held in order to avoid having it fall to the ground or to avoid the need to make a storage action if the handle needs to be released momentarily, as is common during material-shoveling. Too, once stored, the handle must then be retrieved, which is inconvenient. Releasing the handle without stowage causes it to fall to the ground, often creating a hazard during the fall, a tripping hazard afterward, and a potential for ergonomic strain in retrieving the grip handle from a position adjacent to the ground. Though the advantages of these designs are readily apparent their less obvious aspects have apparently prevented these devices from achieving broad acceptance in the marketplace.
Other auxiliary handle designs address and allay such needs for balancing and eliminate the need for continuously holding the hand grip by having the benefit of automatically returning the grip handle to an easily grasped position. These designs are considered self-returning auxiliary handle designs. A number of designs are known. Unfortunately, these designs have design-specific performance shortfalls which either reintroduce a deficit from earlier handle designs, or create new performance and construction issues.
The first of the returnable design examples is by Decker U.S. Pat. No. 4,793,645. This design uses an elastomeric living hinge in an open-mouth bird-beak-like configuration which helps connect the auxiliary handle to the implement and which closes as the auxiliary handle is lifted for use and which returns the handle to its non-loaded condition when released. Though the handle returns to its starting point, the nature of this design, due to its hinge's relatively immovable and definitive line of action, limits the hand grip's lateral freedom of motion in similar aspect to pivotally mounted auxiliary handles. Thus, while such was an improvement for returning the handle, the limited motion of the grip remained.
A second type of returnable handle has fewer limitations on its motion yet significant drawbacks remain, and relate to reorientation of the tool with respect to the ground. These designs are also typically expensive to manufacture and add to the weight of the implement.
These are auxiliary handle designs which are omnidirectional and which return to a starting point using springs or elastomeric elements and are commonly known. Ball U.S. Pat. No. 5,487,577 shows a substantial spring element which provides omnidirectional freedom of motion of a hand grip which is fixed to the top of a shaft, as visually interpreted therein and similar to other known devices, which shaft itself is then connected to the implement through the spring element. Other known devices are of similar construction. Observation of users shows that rotation of the fixed grip member about its own axis is immediately and substantially transferred into a highly undesirable rotation effect on the implement about the implement's predominant longitudinal axis, thereby changing the orientation of the tool portion of the implement with respect to the ground. While this could be helpful in some circumstances, the unintended and undesired result is typically that the load is unintentionally dumped as for a shovel, or in cutting too close to the ground as in a vegetative trimmer. In order to overcome this undesired situation users are typically required to adopt awkward postures and to make unnatural motions and must take unusual care to avoid rotation of the hand grip so that the implement stays usefully oriented. This inability of being able to perform such natural motions requires constant mental effort and user-attention to maintain. As well, it is frustrating and productivity hindering during lapses of focus that then result in mistakes and poor task actions. Such unnatural grip orientation requirements also results in the repetitive-use of a substantially single-set of muscles of the forearm of the grip-hand, and thus is physically straining and tiring.
Another ergonomic result of such unnatural grip orientation is that it tends to cause the user to pronate the wrist at a ninety degree angle when tossing a load forward as for a shovel or when reaching as for a vegetation trimmer. This effect is due to the combination of the user's firm grip on the auxiliary handle in order to controllably hold it and the need for the grip to maintain a non-rotated orientation so to maintain tool orientation. A possible solution to this pronation would be to provide a hand grip which could rotate generally about its axis. Such a modification would allow the grip hand to move into alignment with the forearm during such toss and reach motions, thereby eliminating or assuaging the non-ergonomic 90 degree pronating wrist-bend. Unfortunately adding such swiveling features to the hand grip and its mounting to allow such hand-rotation is technically difficult, costly to manufacture, and prone to performance issues such as jamming or excessive looseness and poor ergonomic feel. It is also notable that for such omnidirectional or similar spring-loaded-like designs, if the grip handle is simply released, it can snap-back to the main handle and to the user's body with much force and can cause injury or hazardous evasive action. Furthermore, this effect is largely dependent on the choice of connecting element, which for such design configurations must be fairly substantial for reliability performance reasons such that such snap back seems nearly unavoidable.
Another notable feature of such stiff, returnable omnidirectional type auxiliary handle constructions is that lateral motion of the hand grip to any position other than directly over the implement main handle results in an undesirable rotation of the implement and reorientation of the implement's tool portion relative to the ground similar to the effect of rotating the fixed hand grip. This motion is also similar to pivotally attached auxiliary handle designs and so is a surprising and unexpected undesirable result given the appearance of such devices to the contrary.
This surprising action arises and is thought to be explained as follows: when performing a typical lifting action, as the user's hands which are gripping the implement and the auxiliary hand-grip are moved in the principal lifting or typical forward-tossing-motion and direction-of-use they tend to oppose each other directly and thus the effort of one hand can oppose the effort of the other and allow the substantial spring element to be overcome to allow the auxiliary handle to be raised away from and returned to the implement main handle. Taking this concept one step further, one notices that when such auxiliary-grip is moved laterally there is effectively no appreciative opposing force other than the leverage effect of the load on the tool and/or the user's hand gripping the implement main handle to counteract or bear against the substantially stiff connecting element as the users auxiliary grip hand naturally moves laterally to tilt or cant the auxiliary handle to sideward during-use. Such motion tries to force the spring element into further bending and in a different direction so that the lateral motion of the auxiliary hand, rather than producing a further bend in the element in a lateral direction, such lateral movement (of the auxiliary grip), is converted into rotation of the implement, which is typically undesirable.
As well, a surprisingly hidden contributing factor, and perhaps more explanatory for such rotations, is that while the spring or stiff bending-element is in the bent state and with the auxiliary handle moving laterally, the spring's bent shape acts as a kind of an L-shaped mechanical-crank which is integral throughout its shape, and because of this, the sideways lever motion of the auxiliary handle is transmitted directly and immediately to the implement main handle through the spring and main-handle connection. Similarly interesting, for a torque applied to a fixed auxiliary handle connected to such a spring or omnidirectional linkage, the applied torque operates in a manner much like a rotary linear transmission made from a long spring in a nonfunctional casing much like those typically used on electric drills for fine polishing or grinding wherein a torque at one end is output as rotation at the other end, thereby auxiliary handle grip rotation would be inducing rotation of the implement and hence also its tool portion, which can create fatigue and ergonomic strain to accuracy control to maintain job performance. As well, it is thought that such a sideward handle motion acting on any bent flexible cylindrical item will to some extent naturally induce a torsion and differential twisting within such item and which torsion, depending on apparatus-construction, would necessarily be transferred and act on the ends of the item, and which general effect might be explained in a manner much like the wire strand in the coil of a spring under load and which internal-torsion mechanical-effect or mechanism, if present, may also contribute to the implement rotation effect observed.
Reflecting on the undesired implement rotation effects of such constructions of omnidirectional, self-returning, auxiliary handle devices it appears that these devices were developed mainly as a way to overcome the load balancing and handle grasping deficits of the omnidirectional auxiliary handles which came before them. It is notable that it appears that most all omnidirectional auxiliary handle devices which return to their starting point provide some useful benefit yet remain comprised of many parts, add weight to the implement, are costly and difficult to manufacture and install, and suffer from one or more alternate compensating performance deficits, and could be physically hazardous to the user. Characteristics such as these seem to have prevented these self returning devices from achieving widespread success, much like the others.
As well, as review, and in general, many of the previous auxiliary handle designs to-date have substantial performance and ergonomic deficits in addition to being costly to manufacture, are difficult to install, require tools to install, require modification of the implement to install, add to the weight of the implement, require stowage of the handle upon release, provide difficulty in controlling the implement, require continuous balancing of the implement, or require refraining from certain highly-desired and comfortable motions.
It is, therefore, desirable to develop an auxiliary handle for hand held implements which solves most, if not all, of the preceding problems.